If there are four national languages, I'd say it would be in your own interest to be fluent or at least capable in all of them. As I understand it, Switzerland is about two-thirds "Germanschweiz" and Swiss German is therefore the most common language spoken in the country. I don't think it is unreasonable for an airline that has to live with that reality, to expect their employees to speak the local language. Remember that you don't only communicate with other crew, but passengers, other staff, authorities etc. etc.
Besides that, it's an easy filter. If they can't get enough pilots, it will be one of the first requirements that will be waived. Either officially or unofficially. I'd say it's not exactly discriminatory since it's a skill you can acquire. You are not being rejected on a quality that you can't change about yourself such as skin color, nationality, age etc. But hey, that's just me.